1. Field of the Invention
The present invention relates to a charging voltage controller of an image forming apparatus, and more particularly, to a charging voltage controller of an image forming apparatus capable of compensating for a change of a surface electrical potential on a photoconductive medium due to a variety of factors influencing a charging roller.
2. Description of the Related Art
Generally, an image forming apparatus, such as a duplicating machine, a printer, a facsimile, or a multifunction machine, for performing various functions has a printing function. The printer outputs information processed by a computer in a visible form.
FIG. 1 is a schematic cross-sectional view of a charging voltage controller of a conventional image forming apparatus.
Referring to FIG. 1, the image forming apparatus includes a control unit 10, an HVPS (High Voltage Power Supply) 20, a charging device 30, a photoconductive drum 40, a laser scanning device 50, a developer 60, and a transfer roller 70.
With a power supply, the control unit 10 outputs a controlling signal to drive each part of the image forming apparatus while simultaneously applying a pre-set voltage to each corresponding roller of the image forming apparatus.
The HVPS 20 applies a voltage corresponding to the controlling signal provided from the control unit 10 to a charging roller 30a, a developing roller 60a and the transfer roller 70, respectively.
The charging device 30 evenly charges a surface of the photoconductive drum 40 as the charging roller 30a is rotated while being charged with a higher voltage supplied from the HVPS 20. The laser scanning device 50 scans the photoconductive drum 40 with light in response to print data under control of the control unit 10.
The developer 60 develops an electrostatic latent image formed on the photoconductive drum 40 by the laser scanning device 50 with a developing agent having an electric charge using the developing roller 60a which is rotated while being charged with a developer voltage supplied from the HVPS 20.
The transfer roller 70 is rotated by the photoconductive drum 40 while being charged with a transcription voltage applied from the HVPS 20, and prints an image developed on the photoconductive drum 40 onto a sheet of paper being fed by a feeding unit (not shown). The image forming apparatus fuses the image printed on the paper by the transfer roller 70 through a fusing unit (not shown) and discharges the paper bearing the fixed image.
In a case that a printing process is performed by the image forming apparatus having the foregoing structure, if the charging potential of the photoconductive drum 40 is uneven, a density deviation occurs in the image printed on the paper, and a print image quality deteriorates.
That is, the surface electric potential of the photoconductive drum 40 can be changed due to an influence of environments (for example, temperature and humidity) where the image forming apparatus is used. Also, a film thickness of the photoconductive drum 40 becomes thinner as a result of a longer usage, thereby changing the surface electric potential. The change in the surface electric potential could deteriorate an image quality. Therefore, it is necessary to maintain a constant surface electric potential of the photoconductive drum 40 and prevent deterioration of the image quality.